There are an estimated 100,000,000,000 neurons in the human connectome; a synapse is a connection from one of them to another, therefore:

99,999,999,999:99,999,999,998 might identify a synapse were there only one synapse possible per pair of synapses. But there could be more than one. Since there are a few quadrillion synapses, storage holding a number like 9,999,999,999,999,999 ought to be able to able to be enumerative of them.

99,999,999,999:99,999,999,998;9,999,999,999,999,99 9 ought to be sufficient to store an identification for each synapse (fifty-one digits) - with the hope of whether one could reliably enumerate a specific neuron's synapses. Such might not be possible, however the following elaboration relies thereon:

Fifty-one digits is sufficient to identify each of the quadrillion synapses and a list containing all the synapses would be fifty-one quadrillion bytes long. We will only need to place one digit in one byte at this time. In order for representation of each synapse to be stored as implied above, we will need about 1,001 terabyte hard drives. They are in the neighborhood of $30 per terabyte these days - so such a storage device would cost about $50,000.